Various technologies for monitoring the state of a predetermined area have been developed. For example, Japanese Patent No. 5456414 (PATENT LITERATURE 1) discloses the following technology: an area-monitoring display method in which values or changed values regarding at least one kind of certain events are measured by a plurality of sensors arranged at various places in a monitoring target area, data obtained through the measurement is processed, and the processed results are displayed on a monitor screen, wherein the processed results are displayed so as to overlap an area display indicating the monitoring target area, and the positions of the processed results displayed on the area display on the monitor screen are set to be the positions that correspond or substantially correspond to the arrangement places of the sensors with respect of which the processed results have been obtained. In the area-monitoring display method, a circular shape is used as a display shape of each processed result, the center of the displayed circular shape indicates the measurement place, the size of the circular shape indicates the magnitude (absolute value) of the measurement value, and the color of the circular shape is translucent such that the processed result displayed so as to overlap the measurement place on the display of the monitoring target area can be seen.